Field emission devices (FEDs) or micro-vacuum tubes have many advantages over conventional semiconductor silicon devices for signal and data processing. For example, FEDs are much faster switching in the terahertz regime, are temperature and radiation tolerant, and are relatively easy to construct, requiring the disposition of appropriate layers of interleaved metals and insulators above a supporting substrate. Recognized applications range from discrete active devices to high density SRAMs and displays, radiation hardened military applications and temperature insensitive space technologies, etc. The literature on field emission devices, which is extensive, principally (if not totally) focuses on unidirectional emission devices. Typically, such prior art devices include a cathode, a gate to aid in controlling the emissions of the cathode, and an anode. With only these three dedicated electrodes the resultant device is necessarily application limited.
Activity in the field of cold cathode emission at VLSI levels has been increasing in the past few years. (For example, certain novel lateral field emission device structures and methods of fabricating the same are presented in a co-pending, commonly assigned U.S. patent application, Ser. No. 07/722,768, now U.S. Pat. No. 5,233,263 entitled "Lateral Field Emission Devices and Methods of Fabrication," the entirety of which is hereby incorporated herein by reference.) The present application is believed to further advance the state of the art by providing novel bidirectional field emission devices which more closely mirror the capabilities of a conventional, silicon-fabricated field effect transistor.
As an example of one application, a significant number of publications have proposed using certain existing field emission devices for SRAM cells. However, few (in any) proposals for using a field emission device structure for a DRAM cell have been expressed. The disadvantage to the traditional FED for use as a DRAM cell relates to its inherent unidirectional nature. By providing a bidirectional field emission device, however, a cell can be designed such that the cell state (`1` or `0`) will be a stored charge on an addressable device. The device state can then be queried to ascertain the stored result.
Thus, to further continue advancement of field emission technology, a genuine need exists in the art for bidirectional field emission devices and for methods of fabricating the same. With a bidirectional FED, multiple applications become possible, including the unique use thereof in a DRAM cell structure.